1. Field of the Invention
The present invention relates to a method of operating a pneumatic transport system in a process line of a spinning mill, for example a cleaning line or blow room line which extends from a bale opening machine via cleaning machines and/or mixing machines and/or metering machines to a carding system, optionally with autonomously operating regions, wherein fiber flocks are transported through ducts by means of airflows generated by fans and these airflows can be influenced by units such as fans, adjustable flaps, leakage air openings and induction boxes. The present invention also relates to an apparatus for carrying out the method.
2. Description of Related Art
The operation of a pneumatic transport system in a process line of a spinning mill has a decisive effect on the efficiency of the treatments carried out by the process line. The incorrect adjustment of the various fans, adjustable flaps and leakage air supply orifices not only leads to an undesired increase in the energy costs but also to performance penalties in the various treatment units. For example, it is important in a coarse cleaning machine to provide the correct static pressure conditions for the operation of the coarse cleaning unit. If the pressure is too high, then this leads to the generation of dust and too much waste material, i.e., exploitable product material is lost with the waste. If, on the other hand, the pressure is too low, then the waste material with dust can be sucked in again so that the cleaning action leaves something to be desired.
In spinning mills the operators are afraid, above all, of blockages which can arise through accumulations of fiber flocks. In order to counteract blockages, the basic settings of the suction fans which are preferably used are frequently set to a maximum in practical operation, although this is not correct for the technology of the treatments which are to be carried out. As a result, unnecessarily high energy costs are caused and the performance or efficiency of the treatment unit is reduced. The problem is particularly acute in cases where several units are provided which influence the pressure in critical regions, and indeed because the adjustment of the one unit frequently causes an effect at other units which is not properly taken into account by the operator.
The object of the present invention is to so develop a method or apparatus of the initially named kind where one achieves a correct adjustment of the adjustable units in a relatively simple way using relatively simple means, i.e., achieves an adjustment which, on the one hand, reduces the energy costs but, on the other hand, ensures that the treatments which are to be carried out can be carried out with a high degree of efficiency. At the same time the method or apparatus of the present invention should make it possible to monitor the pressure conditions and also to prevent the occurrence of blockages.
In order to satisfy this object method-wise one proceeds in accordance with the invention in such a way that
a) in critical regions the respectively prevailing static pressure is measured by means of pressure sensors and, in so far as this pressure lies outside of a predetermined desired range, a correction is first made at one of the units which contributes to determining this pressure in the sense of changing the pressure into the desired range or in the direction towards the desired range,
b) in that the effect of this change in other critical regions affected thereby is determined with respect to the pressure measured there and a change is subsequently effected of a further unit responsible for the pressure in these regions,
c) in that the steps a) and b) are repeated if required, eventually while changing the settings of other units, in the sense of an iterative adaptation to the desired ranges, i.e., until the measured pressures lie in the respectively provided desired ranges.
The regulation steps should preferably be so effected that any short term fluctuations which occur are ignored.
Through the use of an iterative method of this kind, one succeeds in bringing the pressure values in the critical regions into the respectively predetermined desired ranges, although the adjustments of the individual units lead to pressure changes in a plurality of critical regions. The adjustment is also made possible by means of relatively simple devices such as pressure sensors and a computer programmed in accordance with the regulation process, with the computer simply calculating the desired values for the adjustment of the individual variable units and with the actual adjustment of these units being effected by the respective machine control which is in any case present. A precondition for the use of this method is solely that for the respectively prevailing rate of production (kg/h) one specifies corresponding desired pressure values for the individual critical regions. This is however normal since in the design of the individual treatment units the designer must always think about the desired or permissible pressure values.
A particularly favorable feature of the method of the invention is the fact that after achieving pressures in the critical regions which lie within the desired ranges the regulation process can be temporarily terminated. The regulation process is thus suitable as one task for a computer which controls the entire system or part of the system. As this one task only takes place when starting up the system, or when a change in production occurs, it is a task which can largely be carried out by the computers which are already present in such systems. Thus, no substantial additional costs arise on realizing the invention.
Since pressure sensors have to be arranged in the critical regions in order to carry out the "optimization phase" when starting up the system, and on a change of the relevant production factors, the same sensors can be used during permanent operation of the system to monitor the operation without significant additional costs. By way of example, the pressure values prevailing in the critical regions can be controlled at intervals of time and, if required, newly set. Corrections are only necessary in exceptional cases, for example when a change in pressure points to the development of a blockage. If one uses the pressure sensors for this purpose then the checks can take place at very short time intervals. Otherwise, it is sufficient to effect the checks at intervals in the range from a day up to several months, preferably once weekly.
After a stop in production or a change of material the adjustment of the pressures should be checked and, if necessary, corrected after restarting production.
As previously indicated the desired ranges should be selected or newly set in accordance with the envisaged production. The method of the invention is usable in all autonomously functioning regions in which several units influence the pressure at the respective critical regions.
In autonomously functioning regions in which only one unit is responsible for the pressure prevailing in a critical region, this unit is separately adjusted, controlled or regulated. In carrying out the method of the invention, it is of advantage for each critical region to effect the first change at the unit which most strongly affects the pressure in this region. One can namely assume, in the sense of the invention, that a change at this unit will have less effect on the pressure values in other critical regions which then ensures that the iterative process converges rapidly and reliably.
Furthermore, the sizes of the changes which are successively effected should be made increasingly smaller in order to achieve a convergent iterative adjustment of the pressures into the desired ranges.
The method of the invention can, in particular, be used in a process line which comprises a bale opening machine which feeds fiber flocks into a duct, a suction ventilator provided in the duct, optionally a metal separating unit and/or dust extracting unit built into the duct, a coarse cleaning unit, a second suction fan and also optionally a fire separating unit with a spark sensor, with processed waste material eventually being fed into the duct between the bale opening machine and the first-named suction fan. The method is then characterized in accordance with the invention in that the pressure of the duct is measured in a first critical region at the outlet of the bale opening machine before the first-named suction fan and before the feed position for any waste which is eventually fed into the duct and also in a second critical region before the second suction fan; in that the pressure is adjusted in the first critical region, principally by changing the displacement rate of the first suction fan; in that the pressure in the second critical region is adjusted by changing the degree of opening of a leakage air orifice which opens into the duct and/or the discharge rate of the second suction fan; and in that the two last named steps are carried out until the pressures prevailing in the first and second critical regions lie within the respective desired ranges.
The fans which are built into the treatment units and which are of importance for the treatment which is carried out, but have, however, little to do with the transport function of the flocks through the process line, are, in accordance with the invention, preferably fixedly set. In a specific embodiment of the invention, the pneumatic transport system is for a process line of a spinning mill in which a bale opening machine feeds fiber flocks into a tubular duct which, when considered in the direction of flow, leads via a first suction fan and, optionally, via a metal separating unit and/or a duct separating unit, via a coarse cleaning unit and via a second suction fan to a flock mixer, with the flocks being separated from the transport air prior to or in the mixer, and wherein a fire separating unit with a spark sensor is optionally provided between the second suction fan and the coarse cleaning unit, wherein a leakage air orifice opens into the duct after the second suction fan and wherein processed waste material can be eventually fed into the duct between the bale opening machine and the first suction fan. Further, pressure sensors are provided in critical regions of the transport system, for example at the point at which flocks are fed from the bale opening machine into the duct and at a position after the coarse cleaning unit and before the second suction fan. A regulating means is provided which can be programmed with respective desired value ranges for each critical region at each envisaged rate of production. An iterative adjustment of the units which influence the respective pressures at the critical regions can be carried out by the regulation system until the pressures lie within the respective desired ranges.
The method of the invention includes the steps of:
(a) measuring, in each of a plurality of critical regions, the respectively prevailing static pressure by means of pressure sensors;
(b) determining whether at least one of the respectively prevailing static pressures is outside of a predetermined desired range;
(c) adjusting at least one of the units in a manner to affect the at least one of the respectively prevailing static pressures to change same in a direction toward or into the desired range, if the at least one of the respectively prevailing static pressures is outside of the predetermined desired range;
(d) determining the magnitude of a change in a prevailing static pressure in at least one further critical region affected by the step of adjusting;
(e) adjusting a further one of the units in a manner to affect the prevailing static pressure in the at least one further critical region to change same toward or into a predetermined desired range for the at least one further critical region, if the prevailing static pressure of the at least one further critical region is outside of the predetermined desired range for the at least one further critical region; and
(f) repeating steps (a) through (e), as necessary, until measured pressures line in the desired ranges. In a further aspect of the invention, short term pressure fluctuations which occur are ignored during the steps of determining.
The method further can include the step of terminating the method after the critical regions lie within respective desired ranges.
Still further, the invention includes the steps of measuring the pressures prevailing in the critical regions at intervals of time and, if any of the prevailing pressures are outside respective desired ranges, performing again the steps of adjusting until prevailing pressures at the critical regions lie within respective desired ranges. The steps of measuring are performed in time intervals in the region from once per day to once per several months, or in the region of once per week.
Further, steps (a) through (f) are performed after a stop in production of the spinning mill or a change in material composition of material transported through the pneumatic transport system.
Still further according to the invention is the step of determining an intended rate of production and setting the desired ranges as a function of the intended rate of production and, further the step of changing a production rate and adjusting prevailing pressures in the critical regions in accordance with the steps of adjusting.
In a further aspect of the invention, the pneumatic transport system further includes autonomously functioning regions of the pneumatic transport system, whereby a plurality of units determine the pressure in the respective critical regions, wherein the method further includes performing steps (a) through (f) in the autonomously function regions.
Further, the system can further include autonomously functioning regions of the pneumatic transport system in which only one unit, respectively, is responsible for the pressure prevailing at a respective critical region, wherein the steps are separately performed for the one unit.
In a still further aspect of the invention, for each of the critical regions, a step of adjusting is first performed for a unit which affects the prevailing pressure to the greatest degree.
The method of the invention can further include the steps of adjusting being performed in a sequence corresponding to an order of critical regions with regard to the direction of flow, beginning at a critical region at which a step of adjusting is first required, as defined in steps (c) and (e).
Still further according to another aspect of the invention, the steps of adjusting include adjusting the units in successively smaller amounts to achieve a converging iterative adjustment of the prevailing pressures into the respective desired ranges.
According to an additional feature of the invention, the bale opening machine feeds fiber flocks into a duct of the pneumatic transport system, the fans include a first suction fan provided in the duct, a coarse cleaning unit, a second suction fan, a means for feeding processed waste into the duct between the bale opening machine and the first suction fan, and wherein:
(i) the step of measuring is performed (1) in a first critical region at an outlet of the bale opening machine upstream of the first suction fan and upstream of the means for feeding processed waste and (2) in a second critical region upstream of the second suction fan;
(ii) the step of adjusting at least one of the units comprises adjusting a displacement rate of the first suction fan for adjusting the prevailing pressure in the first critical region;
(iii) the step of adjusting a further one of the units comprises performing at least one step selected from the group consisting of (1) changing a degree of opening of a leakage air orifice which opens into a duct, and (2) adjusting a displacement rate of the second suction fan for adjusting the prevailing pressure in the second critical region;
the steps (ii) and (iii) are performed repeatedly until measured pressures lie within the desired ranges.
In a still further aspect of the invention, the method further includes the steps of continuously measuring the prevailing pressures; performing at least one step selected from the group consisting of (1) providing a warning signal and (2) discontinuing fiber flock transport upon measurement of a prevailing pressure at an impermissible deviation from a selected pressure.
Further, in an additional aspect of the invention, the method includes the steps of measuring the prevailing pressures at regularly repeating intervals; performing at least one step selected from the group consisting of (1) providing a warning signal and (2) discontinuing fiber flock transport upon measurement of a prevailing pressure at an impermissible deviation from a selected pressure.
In a still further aspect of the invention, at least one of the fans is built into treatment devices of the fiber flocks and does not significantly affect the prevailing pressures.
Still further, in an additional aspect of the invention, the method includes the steps of measuring a pressure differential across at least one of the fans and determining the value of a variable parameter of the at least one of the fans; determining a prevailing volume flow through the at least one of the fans with reference to a performance characteristic of the at least one of the fans, relating pressure differential to volume flow for various settings of the variable parameter; and iteratively varying the variable parameter of the at least one of the fans until a pressure difference is measured which corresponds at a prevailing setting of the variable parameter of the at least one of the fans to a desired volume flow through the at least one of the fans.